The present invention relates to a method for printing bar-codes on a surface of an object, for example, a nuclear fuel cladding tube, by irradiating the surface of the object with laser beams while scanning. In particular, the present invention relates to a bar-code printing method in which not only physical or chemical influences applied to the object to be printed can be reduced but also printing efficiency can be improved.
The assignee of the present invention has already proposed, in Japanese Patent Application No. 7-265971, a method for printing bar-codes on a surface of an object, for example, a nuclear fuel cladding tube, by irradiating the object with scanned laser beams. In the embodiment of this application, each of the thick lines contained in a bar-code is printed by drawing a plurality of thin lines on a circumferential surface of a fuel cladding tube leaving no interval between them.
According to this bar-code printing method, because the bar-codes are printed by changing the physical or chemical characteristics of the surface of the cladding tube, it is possible to improve the durability and the permanence of the bar-codes; therefore, from this point of view, this method is desirable for printing on fuel cladding tubes the information for the maintenance thereof. In contrast, in the case where bar-codes are printed with an ink as is conventional, such bar-codes do not have sufficient durability and permanence in comparison with those printed by laser beams.
However, the above-described bar-code printing method using laser marking has a certain problem. That is, since high reliability is strongly required in the cladding tube, the physical or chemical influence applied to the cladding tube should be reduced to as low as possible, and, in order to meet this requirement, a decrease in the clarity of the bar-codes is inevitable. Furthermore, because a large number of thin lines should be drawn to make each thick line, the printing speed and efficiency is difficult to improve.